added bit-exact tests for RGB2Gray

Author: Rostislav Vasilikhin

modules/imgproc/test/test_color.cpp

@@ -455,7 +455,7 @@ void CV_ColorGrayTest::get_test_array_types_and_sizes( int test_case_idx, vector
 double CV_ColorGrayTest::get_success_error_level( int /*test_case_idx*/, int i, int j )
 {
     int depth = test_mat[i][j].depth();
-    return depth == CV_8U ? 2 : depth == CV_16U ? 16 : 1e-5;
+    return depth == CV_8U ? 1 : depth == CV_16U ? 2 : 1e-5;
 }
 
 
@@ -2844,6 +2844,11 @@ void runCvtColorBitExactCheck(ColorConversionCodes code, int inputType, uint32_t
     }
 }
 
+TEST(Imgproc_cvtColor_BE, COLOR_RGB2GRAY)  { runCvtColorBitExactCheck(COLOR_RGB2GRAY,  CV_8UC3, 0x416bd44a); }
+TEST(Imgproc_cvtColor_BE, COLOR_RGBA2GRAY) { runCvtColorBitExactCheck(COLOR_RGBA2GRAY, CV_8UC3, 0x416bd44a); }
+TEST(Imgproc_cvtColor_BE, COLOR_BGR2GRAY)  { runCvtColorBitExactCheck(COLOR_BGR2GRAY,  CV_8UC3, 0x3008c6b8); }
+TEST(Imgproc_cvtColor_BE, COLOR_BGRA2GRAY) { runCvtColorBitExactCheck(COLOR_BGRA2GRAY, CV_8UC3, 0x3008c6b8); }
+
 TEST(Imgproc_cvtColor_BE, COLOR_BGR2YUV) { runCvtColorBitExactCheck(COLOR_BGR2YUV, CV_8UC3, 0xc2cbcfda); }
 TEST(Imgproc_cvtColor_BE, COLOR_RGB2YUV) { runCvtColorBitExactCheck(COLOR_RGB2YUV, CV_8UC3, 0x4e98e757); }
 TEST(Imgproc_cvtColor_BE, COLOR_YUV2BGR) { runCvtColorBitExactCheck(COLOR_YUV2BGR, CV_8UC3, 0xb2c62a3f); }